1. Field of Invention
The current invention relates generally to apparatus, systems and methods for controlling waves. More particularly, the apparatus, systems and methods relate to steering (e.g., scanning) achromatic waves using one or more prisms. Specifically, the apparatus, systems and methods provide for steering achromatic beams with a triplet pairs of prisms so that the beams behave as though they are monochromatic.
2. Description of Related Art
In modern optical sensors and imaging systems it is often desirable to steer or deflect incoming beams of light in order to capture data in multiple fields of the beam. This beam steering, also known as beam scanning, is conventionally performed using a Risley prism scanner. FIG. 1 illustrates a prior art Risley prism pair. A Risley prism scanner is an optical device comprised of two identical prisms placed into an optical beam such that the prisms can be rotated about an axis parallel to the optical beam. This action results in the steering of the beam as it leaves the prism pair, and for example, can act as a beam steering device to direct a laser beam into the far-field through a large steerable angle, characteristic of each prism's makeup of optical material and wedge angle.
However, because the index of refraction of an optical material is a strong function of the wavelength (color), the amount of deflection interposed on the beam varies strongly with wavelength. Although this is a useful phenomenon in some circumstances, it is highly undesirable in many others because it limits the spectral bandwidth of beams that are steerable using a conventional Risley prism scanner. For this reason, conventional Risley prism scanners are only useful for monochromatic systems, such as single-wavelength laser systems or optical imaging systems having very narrow bandpass filters. A need therefore exists for a device, system and/or apparatus that is capable of steering an achromatic beam so that the beam behaves as if it were a monochromatic beam.